The present invention relates to a down-the-hole drill (“DHD”) hammer. In particular, the present invention relates to a DHD hammer's actuator assembly having a reverse exhaust system.
Typical DHD hammers include a piston that is moved cyclically with high pressure gas (e.g., air). The piston generally has two end surfaces that are exposed to working air volumes (i.e., a return volume and a drive volume) that are filled and exhausted with each cycle of the piston. The return volume pushes the piston away from its impact point on a bit end of the hammer. The drive volume accelerates the piston toward its impact location.
Typical DHD hammers also combine the exhausting air from these working air volumes into one central exhaust gallery that delivers all the exhausting air through the drill bit and around the externals of the DHD hammer. In most cases, about 30% of the air volume is from the DHD hammer's return chamber, while about 70% is from the hammer's drive chamber. However, this causes much more air then is needed to clean the bit-end of the hammer (e.g., the holes across the bit face). Such high volume air passes through relatively small spaces creating high velocity flows as well as backpressure within the DHD hammer. This is problematic as such high velocity air along with solids (i.e., drill cuttings) and liquids moved by the high velocity air causes external parts of the DHD hammer to wear rapidly while backpressures within the DHD hammer reduces the tool's overall power and performance.
A DHD hammer, such as the present invention, having a reverse exhaust system reduces the amount of high velocity air along the bit-end thereby reducing the overall wear on the DHD hammer. Moreover, the present invention provides for reduced backpressures within the DHD hammer that allows for improved power and performance of the tool.